Sensors having motion-detecting functions for sensing entries of people and the like have conventionally been known. While such a sensor is required to have a sufficient detection accuracy, using a thermal image sensor such as a thermopile or a bolometer array alone may fail to distinguish a remote adult and a nearby child from each other, for example. Hence, for example, techniques set forth in Patent Literatures 1 to 3 propose composite sensors each combining a thermal image sensor and a range image sensor together.